Controlling the ratio of amplification factors between linear amplifiers

ABSTRACT

An electronic device where the ratio between two amplification factors of two amplifiers, called main amplifiers, is adjusted using a control means. The control means constantly equalizes the output signals of the two main amplifiers by adapting one of the control signals. The output signals are acted on in order to adjust the control signals. Owing to the fact that the input signals are in a ratio N, this same ratio is obtained between the amplification factors of the two main amplifiers. The two main control signals, used to control the main amplifiers, are employed for controlling any other amplification factor of at least two other amplifiers or groups of amplifiers, so as to establish a ratio N between these other amplification factors. The main circuit thus allows N to be applied and regulated between the amplification factors of other amplifiers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to French Patent Application No.0513489, filed Dec. 30, 2005, entitled “METHOD FOR CONTROLLING THE RATIOOF THE AMPLIFICATION FACTORS OF TWO LINEAR AMPLIFIERS, AND DEVICE FORSAME”. French Patent Application No. 0513489 is assigned to the assigneeof the present application and is hereby incorporated by reference intothe present disclosure as if fully set forth herein. The presentapplication hereby claims priority under 35 U.S.C. §119(a) to FrenchPatent Application No. 0513489.

TECHNICAL FIELD

The present disclosure relates to amplifiers and, notably, to thecontrol of the ratio between the amplification factors of at least twoamplifiers with controllable amplification factors such as, for example,linear amplifiers.

BACKGROUND

Conventionally, a receiver unit includes various filters whose cut-offfrequency must be very precisely fixed. However, by reason oftemperature variations or of the variations, for example, in the powersupply voltage, the parameters of the filters used exhibit very widevariations typically between 40% and 50%.

In order to limit these variations, the filter cut-off frequency iscontrolled by a control signal delivered by another system called amaster system. This conventional filter structure is described, forexample, in the article ‘Integrated Continuous-Time Filter Design—AnOverview’, Yannis Tsividis, IEEE Journal of Solid-State Circuits, vol.29, no. 3, Mar. 1997, pp. 166-176. The master system may include forexample, a phase-locked loop operating according to a stable referencefrequency delivered by an external component such as, for example, aquartz oscillator. The master system includes linear amplifiers that areidentical to (or possibly homothetic with) those incorporated into thefilter, and with an amplification factor that is internally controlledby the same signal used for controlling the cut-off frequency of thefilter.

This control of the master/slave type (the slave being the filter)typically allows a precision of around 5%. Furthermore, in order to makethe filter operate over various frequency ranges, a divider or amultiplier by N may be used between the control signal output from themaster system and the control signal of the filter, if the relationshipbetween the amplification factor of the amplifiers incorporated in thefilter and its control quantity is perfectly proportional. Thus, theratio N may be introduced between the amplification factor of the mastersystem amplifiers and the amplification factor of the amplifiers of thefilter.

Owing to the relationship between the amplification factor and thefrequency (detailed herein below), the cut-off frequency of the latteris varied as a function of the oscillation frequency of the mastersystem, in the same ratio N. Accordingly, if V denotes the controlsignal output from the master system, k is the amplification factor ofthe ideal amplifiers used in the filter and the master system, and bythe relationship k=A*V, where A is the coefficient linking the controlsignal, then Equation 1 below results. $\begin{matrix}{f_{osc} = {{\frac{A \cdot V \cdot k}{2\pi\quad C}\quad{and}\quad{fc}} = \frac{A \cdot V \cdot k}{{N \cdot 2}\pi\quad C}}} & \left( {{Eqn}.\quad 1} \right)\end{matrix}$

In Equation 1, f_(osc) is the master system oscillation frequency, f_(c)the filter cut-off frequency and C a reference capacitance value for thedevice in question (master system or filter to be controlled). Usingthese relationships, Equation 2 results.f _(c) =f _(osc) /N   (Eqn. 2)

In other words, by controlling and adjusting the amplification factor kof the amplifiers incorporated into the filter by means of a controlsignal such as that described hereinabove, a ratio of N is establishedbetween the amplification factors of the master system and of thefilter, and hence the oscillation frequency of the master system and thecut-off frequency of the filter.

However, the relationship of proportionality between the value of thecontrol signal of the amplifier and its actual amplification factor isnever perfect. For example, non-linearities in the control of theamplifier always exist and thus lead to the impossibility of usingdirectly the principle stated hereinabove between the theoreticalrelationship of proportionality and that observed between theoscillation frequency of the master system and the cut-off frequency ofthe filter, in this example.

There is therefore a need for a device that is capable of establishing aration N between two amplification factors, and more particularly, adevice capable of establishing two frequencies which are independent ofthe non-linearity phenomena in the control of the amplifiers.

SUMMARY

The present disclosure provides a device capable of establishing a ratioN between at least two amplification factors, and consequently twofrequencies, which is independent of the non-linearity phenomena in thecontrol of the amplifiers. The present disclosure also provides a devicethat allows a filter cut-off frequency to be controlled by means of astable external signal, in particular when a division or multiplicationratio is introduced between the filter cut-off frequency and theexternal frequency.

In one embodiment, the present disclosure provides an electronic devicehaving a main circuit. The main circuit includes at least two mainlinear amplifiers each having a respective amplification factor and eachrespectively controllable by two main control signals. Each of the mainlinear amplifiers can respectively receive two input signals and delivertwo output signals, the levels of the two input signals being in a ratioN. The main circuit also includes a controller to adjust the value of atleast one of the two main control signals in such a manner as toequalize the output signals, the two amplification factors then being inthe same ratio N.

In another embodiment, the present disclosure provides a method ofcontrolling the ratio of amplification factors of controllable linearamplifiers. The method includes adjusting N to a desired value. N is theratio between the respective amplification factors of two main linearamplifiers that are controllable by two main control signals. Theadjustment is accomplished by receiving two input signals and thedelivery of two output signals by the main amplifiers, where the levelsof the two input signals being in a ratio of N. The adjustment alsoincludes controlling one of the two main control signals so as toequalize the output signals, where now the two amplification factors arein the same ratio N.

In still another embodiment, the present disclosure provides a maincircuit with a differential architecture. Thus, the input and outputsignals are of differential quantities. The main circuit includes atleast two main linear amplifiers each having a respective amplificationfactor and each respectively controllable by two main control signals.Each of the main linear amplifiers can respectively receive two inputsignals and deliver two output signals, the levels of the two inputsignals being in a ratio N. The main circuit also includes a controllerto adjust the value of at least one of the two main control signals insuch a manner as to equalize the output signals, the two amplificationfactors then being in the same ratio N. The controller includes afeedback circuit to control the value of one of the control signals tothe difference between the two output signals.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure and its features,reference is now made to the following description, taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 describes schematically an embodiment of a main circuit accordingto the present disclosure;

FIG. 2 describes in more detail an embodiment of a main circuitaccording to the present disclosure;

FIG. 3 describes more particularly an example of a part of a linearamplifier incorporated in a device, according to the present disclosure;

FIG. 4 illustrates an electronic device incorporating two embodiments ofauxiliary circuits according to the present disclosure;

FIG. 5 illustrates another embodiment of a device incorporating twoembodiments of auxiliary circuits according to the present disclosure;

FIG. 6 illustrates an embodiment of a part of an auxiliary circuitaccording to the present disclosure; and

FIG. 7 illustrates an auxiliary circuit according to the embodiment ofthe device presented in FIG. 5.

DETAILED DESCRIPTION

The present disclosure provides an electronic device where the ratiobetween two amplification factors of two amplifiers, called mainamplifiers, is adjusted using a control means. The control meansconstantly equalizes the output signals of the two main amplifiers byadapting one of the control signals. In contrast to conventionalsolutions, the output signals are acted on in order to adjust thecontrol signals. Owing to the fact that the input signals are in a ratioN, this same ratio is obtained between the amplification factors of thetwo main amplifiers. The two main control signals, used to control themain amplifiers, may be employed for controlling any other amplificationfactor of at least two other amplifiers or groups of amplifiers,respectively of the same type and same structure as the main amplifiers,so as to establish a ratio N between these other amplification factors.In such an application, the main circuit forms a regulation core of theratio N, which allows a ratio N to be applied and regulated between theamplification factors of other amplifiers.

Accordingly, in contrast to conventional solutions that use two controlsignals linked by a proportionality factor, embodiments of the presentdisclosure decouples these two control signals and adjusts the ratiobetween two amplification factors by means of another circuit (theregulation core) that regulates this ratio using a control means actingon two other quantities, in the present case the output signals of themain amplifiers.

In FIG. 1, the main circuit CIP 100 includes a first main linearamplifier AP1 102 controlled by a main control signal Vcde1 104, here acontrol voltage. The control signal Vcde1 104 is, in principle,arbitrary, but must belong to the domain of operation of the mainamplifier AP1 102. The main circuit CIP 100 also comprises a second mainlinear amplifier AP2 106 controlled by a second main control signalVcde2 108, here a voltage.

The second main amplifier AP2 106 receives a reference signal, here avoltage vdc delivered by a generator GEN 110, at its input. This voltagevdc has an arbitrary value belonging to the domain of operation of themain amplifiers AP1 102 and AP2 106 and is of the form referred to as‘small signal’, in other words that it is formed by a static value andcan have a small dynamic variation around this static value. The voltagevdc is delivered to a divider DAC 112 that is programmable using n bits.The divider DAC 112 then delivers an output voltage equal to vdc/N, Nbeing the division ratio of the divider DAC 112.

The division ratio N is a real number. As a variant, a multiplier by Ncould be used. The first main amplifier AP1 102 receives the dividedvoltage vdc/N at its input and delivers a current i1 at its output. Withregard to the second main amplifier AP2 106, this delivers a current i2.In the case of main amplifiers AP1 102 and AP2 106, of thetransconductance type (which is the case for all the amplifiershereinafter cited as examples) , having respective transconductances gm1and gm2, the following relationships, Equations 3 and 4, hold true.i2=gm2.vdc   (Eqn. 3)i1=gm1.vdc/N   (Eqn. 4)

Consequently, equalizing the currents i1 and i2 leads to Equation 5.gm2=gm1/N   (Eqn. 5)

Thus, in order to obtain the ratio N between the two transconductancesof the two main amplifiers AP1 102 and AP2 106, it suffices to equalizethe two current i1 and i2. For this purpose, the two currents i1 and i2are delivered to control means MC 114. The control means MC 114 deliverat the output the control voltage Vcde2, which is a function of thedifference existing between the output currents i1 and i2, in such amanner as to modify gm2, and hence i2, so that it is equal to i1. Inthis way, the two main amplifiers AP1 102 and AP2 106 now have twotransconductances in the ratio N.

Reference is now made to FIG. 2 that details one embodiment of thecontrol means MC 114 of the main circuit CIP 100. For this embodiment,the circuit CIP 100 is considered to have a differential architecture.The correction means MC 114 here form feedback control means for thecontrol signal Vcde2. They comprise generation means MEL 202 whichcorrespond, in this example, to addition means. They comprise a firstnode n1 between the second output of the main amplifier AP2 106 and thefirst output of the main amplifier AP1 102, in such a manner as togenerate a signal, here a current, equal to Equation 6. $\begin{matrix}\frac{\left( {{i\quad 1} - {i\quad 2}} \right)}{2} & \left( {{Eqn}.\quad 6} \right)\end{matrix}$

The generation means MEL 202 also comprise a second node n2 connectingthe first output of the main amplifier AP2 106 to the second output ofthe main amplifier AP1 102 so as to generate a current equal to Equation7. $\begin{matrix}\frac{\left( {{i\quad 2} - {i\quad 1}} \right)}{2} & \left( {{Eqn}.\quad 7} \right)\end{matrix}$

In the case of a negative ratio N, those skilled in the art should knowhow to adapt the generation means MEL 202 by replacing the additionmeans with subtraction means. Similarly, those skilled in the art willknow how to adapt the generation means MEL 202 in the case where theoutput signal quantities from the main amplifiers AP1 102 and AP2 106are voltages.

The two currents generated by the generation means MEL 202 are deliveredto a correction unit BCOR 204 capable of applying, in this example, acorrection of the proportional-integral type. An operational amplifierAOP 206 receives the two currents generated by the generation means MEL202 at its inputs.

The correction unit BCOR 204 also comprises two resistors R1 and R2,here of the same value R, respectively connected between each input ofthe operational amplifier AOP 206 and a common-mode voltage generatorGMC 208 delivering a voltage vmc and connected to ground. Thedifferential voltage across the terminals of the AOP 206 is thereforeequal to R(i2−i1).

The generator GMC 208 can be formed, for example, by means of a currentsource SC 210 connected to a transistor TSC 212 whose control electrodeis fed back onto the electrode connected to the source SC 210, the lastelectrode being connected to ground. The correction integral isperformed by means of two capacitors C1 and C2, here of the same value,respectively connected between the inverting input and the output of theoperational amplifier AOP 206 and between the non-inverting input andthe ground of the operational amplifier AOP 206. This correction allowsthe signal delivered at the output to be stabilized.

Finally, the correction means MC 114 comprise a feedback control loopBCL 214 connecting the output of the operational amplifier AOP 206 tothe control input of the second main amplifier AP2 106. It should beunderstood that the respective roles of amplifiers AP1 102 and AP2 106may be interchanged. By way of example, the voltage vmc can be equal toaround 0.8 V, the resistors R1 and R2 can be around 20 kQ, thecapacitors C1 and C2 around 10 pF, and the gain of the operationalamplifier AOP 206 is preferably very high, for example equal to around50 dB.

The transconductances of the main linear amplifiers AP1 102 and AP2 106can vary between 10 and 250 μA/V. More generally, the correction unitBCOR 204 can perform a correction of theproportional-integral-derivative type. An example of amplifier withcontrollable transconductance, used to form the main amplifiers AP1 102and AP2 106, is shown in FIG. 3. The amplifier Ap1 300 receives adifferential voltage vd at its input. This is applied between the twocontrol electrodes of two transistors M1 302 a and M2 302 b, here of theNMOS type. Each transistor M1 302 a and M2 302 b is biased by a currentIO respectively delivered by a controlled current source SC1 304 a andanother controlled current source SC2 304 b. The two current sources SC1304 a and SC2 304 b are connected to a power supply terminal deliveringa voltage VCC 306.

The current sources SC1 304 a and SC2 304 b are conventionally formed bymeans of transistors configured as current sources. The two inputelectrodes (here the sources) of the transistors M1 302 a and M2 302 bare common, and the common node is connected to a third controllablecurrent source SC3 308 delivering a current equal to 2*IO. The currentsource SC3 308 is furthermore connected via its other terminal toground. The output current iout is delivered by the main amplifier APi300 and measured between two output electrodes (here the drains) of thetransistors M1 302 a and M2 302 b. This output current iout correspondsto the difference between the current coming from the drains of M1 302 aand of M2 302 b and their biasing currents output from the sources SC1304 a and SC2 304 b, respectively.

For the case where the amplifiers have opposite values oftransconductance, the differential input terminals or the differentialoutput terminals are reversed. The main circuit CIP 100 such as waspreviously described hereinabove allows, notably, two control signals tobe obtained (here Vcde1 and Vcde2) in order to be able to control twoauxiliary linear amplifiers of the same type and same structure as themain amplifiers.

In the case of auxiliary amplifiers with controllable transconductances,the control signals (main ones in the case of the circuit CIP) areapplied to the control terminals of the sources SC1 304 a and SC2 304 b,and more precisely to the control electrodes of the transistors formingthese sources. Those skilled in the art will know how to adapt theapplication of the control signals in the case of transimpedanceamplifiers or amplifiers with voltage/voltage or current/current gains.

By ‘the same structure of two linear amplifiers’ is understood the factthat they are identical or homothetic, in other words that there existsa ratio a between the dimensions of the components of each of theamplifiers (for example, the dimensions W and L of the transistors) andalso between the biasing sources of these amplifiers. Consequently, bymeans of the two main control signals, it is possible to control twogroups of auxiliary linear amplifiers, each group being of the same typeand same structure as one of the main linear amplifiers of the circuitCIP 100, such as is defined hereinabove.

Given that these two groups of auxiliary linear amplifiers are of thesame type, have the same structure as the main linear amplifiers andthat their control signals are the same, the same ratios can then beestablished between the amplification factors of the auxiliaryamplifiers of each group as that existing between the main linearamplifiers. Examples of devices using the main control signals Vcd1 andVcd2 are described hereinafter.

In FIG. 4, a device DIS 400 representing a variable-gain amplifier (orVGA) is illustrated, here with differential architecture, formed usingtwo auxiliary circuits CIA1 402 a and CIA2 402 b. The first auxiliarycircuit CIA1 402 a comprises an amplifier AA1 (or transconductor) 404having a controllable transconductance GM1. The transconductor AA1 404receives an input voltage Vi at its differential input, and iscontrolled by an auxiliary control signal which corresponds to the maincontrol voltage Vcde1. The amplifier AA1 404 is chosen so as to have thesame structure as the main amplifier AP1 102 or 300, such as is definedhereinabove.

The second auxiliary circuit CIA2 402 b comprises a second auxiliaryamplifier AA2 406 whose non-inverting input is connected to theinverting output of the auxiliary amplifier AA1 404, and the invertinginput is connected to the non-inverting output of the auxiliaryamplifier AA1 404. Furthermore, the inverting output of the amplifierAA2 406 is fed back onto its non-inverting input and its non-invertingoutput is connected to its inverting input.

The auxiliary amplifier AA2 406 delivers a voltage Vo at its output. Inaddition, the auxiliary control signal of the auxiliary amplifier AA2406 corresponds to the control voltage Vcde2, the structure and the typeof the auxiliary amplifier AA2 corresponding to those of the mainamplifier AP2 106. The amplifier AA2 406 has a transconductance GM2 and,in this device, plays the role of a resistance whose resistivity isequal to 1/GM2, in such a manner that the voltage gain of thecontrolled-gain amplifier is equal to GM1/GM2.

Owing to the fact that the auxiliary amplifiers AA1 404 and AA2 406 havethe same structure as the main amplifiers AP1 102 or 300 and AP2 10 ofthe main circuit, and that they are respectively controlled by thecontrol signals Vcde1 and Vcde2, then Equation 8 holds. Consequently,the controlled gain GM1/GM2 is equal to N.GM1=N*GM2   (Eqn. 8)

Reference is now made to FIG. 5 which illustrates one embodiment of thedevice 500 according to the present disclosure where the two auxiliarycircuits CIA1 402 a and CIA2 402 b respectively form master means andslave means. The slave means CIA2 402 b here correspond to a controlledfilter whose control allows the cut-off frequency to be stabilized to avalue proportional to a reference frequency output from the master meansCIA1 402 a. The slave means CIA2 402 b receives an input signal Sin atthe input and deliver an output signal Sout at the output.

The auxiliary circuit CIA2 402 b is connected to a main circuit CIP 100from which it receives the main control voltage Vcde2 108, as auxiliarycontrol signal. The circuit CIA2 here comprises filtering means, forexample a low-pass filter.

An example of filter 600 that can be incorporated into the auxiliarycircuit CIA2 402 b is illustrated in FIG. 6. This filter can comprise aninput unit BE 602 formed from a first auxiliary linear amplifier withcontrollable transconductance AA21 604 connected in series with a secondauxiliary controllable linear amplifier AA22 606, whose output is fedback onto its input. It also comprises an output unit BS 608 comprisingan auxiliary linear amplifier with controllable transconductance AA27610, whose output is fed back onto its input.

Between the input unit BE 602 and the output unit BS 608, two units ofthe gyrator type, in other words formed from two auxiliary linearamplifiers with controllable transconductance connected as a flip-flopand having opposite transconductance values, are connected in series.The first structure comprises the auxiliary amplifiers AA23 612 and AA24614 and the second structure comprises the auxiliary amplifiers AA25 616and AA26 618.

A first capacitor CA21 is connected between the node common to the inputunit BE 602 and to the amplifier AA23 612, and ground. Similarly, asecond and a third capacitor CA22 and CA23 are respectively connectedbetween the node common to the auxiliary amplifiers AA23 612 and AA25616 and ground, and between the node common to the auxiliary amplifierAA25 616 and the output unit BS 608 and ground. All of the auxiliaryamplifiers with controllable transconductance of the auxiliary circuitCIA2 402 b are controlled by one and the same auxiliary control signalcorresponding to the main control signal Vcde2 108. For this purpose,they have the same structure and are of the same type as the mainamplifier AP2 106 of the main circuit CIP 100.

Reference is again made to FIG. 5. The auxiliary circuit CIA1 402 a hereforms the master means, whose oscillation frequency is used to feedbackcontrol the cut-off frequency of the filter of the auxiliary circuitCIA2 402 b. The auxiliary circuit CIAL 402 a is formed here from aphase-locked loop PLL 502 constructed in the conventional manner. Thelatter receives a reference frequency Fref, supplied for example by aquartz oscillator, at its input.

The reference frequency Fref is delivered to a phase/frequencydiscriminator PFD 504 connected to a charge pump PC 506 delivering avoltage to a voltage-controlled oscillator VCO 508, via a filter LF 510.The output signal from the oscillator VCO 508 is delivered to the inputof the phase/frequency discriminator via a feedback loop. In addition,the control voltage of the voltage-controlled oscillator VCO 508 isdelivered to the main circuit CIP 100, as main control signal Vcd1, soas to control the first main amplifier AP1 102 or 300.

The oscillator with voltage control 700 is then formed usingcontrollable-transconductance amplifiers, as shown for example in FIG.7. In this example, the voltage-controlled oscillator VCO 508 comprisesa structure of the gyrator type formed from two auxiliary amplifierswith controllable transconductance AA11 702 and AA12 704 connected inseries between two capacitors CA11 and CA12. In addition, a resistance Rof negative resistivity is connected in parallel with the capacitorCA12.

The two auxiliary amplifiers AA11 702 and AA12 704 are controlled by anauxiliary control signal which is the voltage delivered to thevoltage-controlled oscillator VCO 508, and which also corresponds to themain control signal Vcd1. The auxiliary amplifiers used to form thevoltage-controlled oscillator VCO 508 are of the same type and samestructure as the main amplifier AP1 102 or 300.

Reference is again made to FIG. 5. The main circuit CIP 100 allows thecut-off frequency of the filter of the auxiliary circuit CIA2 402 b tobe stabilized and also this cut-off frequency to be varied in such amanner that the filter of the auxiliary circuit CIA2 402 b is able tooperate within various frequency bands. Because of the use of the maincircuit CIP 100, the control signal Vcde2 108 for the cut-off frequencyof the circuit CIA2 402 b is no longer proportional to the controlvoltage Vcd1 of the voltage-controlled oscillator VCO 508, and istherefore no longer sensitive to the linearity problems caused by theapproximation of the proportionality ratio associated with the use of adivider (or multiplier).

The range of the dispersion in the filter characteristics can then bereduced to a percentage of around 2%. Although the examples describedhereinabove implement transconductance linear amplifiers, it is equallypossible to use transimpedance linear amplifiers or those withvoltage/voltage or current/current gains, all these amplifiers having anamplification ratio controllable by a voltage or a current depending onthe embodiment used.

The present disclosure is advantageously, but not exclusively, used intelecommunications systems, notably within receiver units and, inparticular, for the control of cut-off frequencies of filtersincorporating controllable linear amplifiers used within receiver units.

The term ‘amplification factor’ here encompasses notably voltage/voltageand current/current gains, transimpedances and transconductances.Consequently, the embodiments of the present disclosure may be appliedto any type of linear amplifier implementing one of the aforementionedamplification factors and the associated electrical quantities.

It may be advantageous to set forth definitions of certain words andphrases used in this patent document. The term “couple” and itsderivatives refer to any direct or indirect communication between two ormore elements, whether or not those elements are in physical contactwith one another. The terms “include” and “comprise,” as well asderivatives thereof, mean inclusion without limitation. The term “or” isinclusive, meaning and/or. The phrases “associated with” and “associatedtherewith,” as well as derivatives thereof, may mean to include, beincluded within, interconnect with, contain, be contained within,connect to or with, couple to or with, be communicable with, cooperatewith, interleave, juxtapose, be proximate to, be bound to or with, have,have a property of, or the like.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. An electronic device having a main circuit, the main circuitcomprising: at least two main linear amplifiers each having a respectiveamplification factor and each respectively controllable by two maincontrol signals, wherein each of the main linear amplifiers canrespectively receive two input signals and deliver two output signals,the levels of the two input signals being in a ratio N; and a controllerto adjust the value of at least one of the two main control signals insuch a manner as to equalize the output signals, the two amplificationfactors then being in the same ratio N.
 2. The main circuit according toclaim 1 further comprising: a generator to generate a reference signal;and a divider coupled to the output of the generator and configured todeliver the said reference signal divided by N, the input signal of oneof the amplifiers being the reference signal and the input signal of theother amplifier being the reference signal divided by N.
 3. The maincircuit according to claim 1 further comprising: a generator to generatea reference signal; and a multiplier coupled to the output of thegenerator and configured to deliver the said reference signal multipliedby N, the input signal of one of the amplifiers being the referencesignal and the input signal of the other amplifier being the referencesignal multiplied by N.
 4. The main circuit according to claim 1,wherein the controller comprises a feedback circuit to control the valueof one of the control signals to the difference between the two outputsignals.
 5. The main circuit according to claim 1, wherein the feedbackcircuit further comprises: a generator to generate an intermediatesignal representative of the difference between the two output signals;and a correction unit coupled to the generator and configured to effecta correction of the proportional-integral type on the intermediatesignal.
 6. The main circuit according to claim 5, wherein the correctionunit also effects a correction of the derivative type.
 7. The maincircuit according to claim 1, wherein the main circuit comprises adifferential architecture, the input and output signals beingdifferential quantities.
 8. The main circuit according to claim 7,wherein the output signals delivered by the main amplifiers are currentsand wherein the generator further comprises: an adder to add, on the onehand, the value of the current delivered on the first differentialchannel of a first main amplifier and the value of the current deliveredon the second differential channel of the other main amplifier and, onthe other hand, the value of the current delivered on the seconddifferential channel of the first main amplifier and the value of thecurrent delivered on the first differential channel of the other mainamplifier.
 9. The main circuit according to claim 8, wherein thecorrection unit further comprises: an operational amplifier; tworesistors connected between each of the inputs of the operationalamplifier and a common-mode voltage generator; a first capacitorconnected between the non-inverting input of the operational amplifierand ground; and a second capacitor, of the same value as the said firstcapacitor, connected between the output and the inverting input of theoperational amplifier.
 10. The main circuit according to claim 1 furthercomprising: at least two auxiliary circuits each comprising at least oneauxiliary linear amplifier with an amplification factor controllable byan auxiliary control signal, the auxiliary amplifiers of the twoauxiliary circuits respectively having the same structures as those ofthe two main amplifiers, wherein the auxiliary control signalsrespectively associated with the two auxiliary circuits are respectivelyproduced from the main control signals respectively associated with themain amplifiers of corresponding structures.
 11. The main circuitaccording to claim 10, wherein the first and the second auxiliarycircuits respectively comprise a first and a second auxiliary linearamplifier connected in series, the output of the second auxiliary linearamplifier being fed back onto its input.
 12. The main circuit accordingto claim 10, wherein the first auxiliary circuit forms a slave means,which comprises a filter incorporating at least one auxiliary linearamplifier, and wherein the second auxiliary circuit forms a mastermeans, to control feedback controlling the cut-off frequency of thefilter, and which comprises a phase-locked loop comprising avoltage-controlled oscillator constructed using at least two linearamplifiers controlled by the auxiliary control signal associated withthe said second auxiliary circuit, and wherein the auxiliary controlsignal associated with the said second auxiliary circuit being deliveredto the main circuit so as to form the control signal for the mainamplifier receiving the reference signal divided or multiplied by N. 13.A method of controlling the ratio of amplification factors ofcontrollable linear amplifiers, the method comprising: adjusting N to adesired value, wherein N is the ratio between the respectiveamplification factors of two main linear amplifiers that arecontrollable by two main control signals, wherein the adjustment furthercomprises: receiving two input signals and the delivery of two outputsignals by the main amplifiers, the levels of the two input signalsbeing in a ratio of N; and controlling one of the two main controlsignals so as to equalize the output signals, the two amplificationfactors then being in the same ratio N.
 14. The method according toclaim 13, wherein the controlling step is accomplished with controllableamplification factors from an auxiliary control signal, wherein thecontrollable linear amplifiers respectively have the same structures asthat of the main amplifiers, and wherein the auxiliary control signalsare generated from the main control signals respectively associated withthe main amplifiers of corresponding structures.
 15. A main circuit witha differential architecture, the input and output signals beingdifferential quantities, the main circuit comprising: at least two mainlinear amplifiers each having a respective amplification factor and eachrespectively controllable by two main control signals, wherein each ofthe main linear amplifiers can respectively receive two input signalsand deliver two output signals, the levels of the two input signalsbeing in a ratio N; and a controller to adjust the value of at least oneof the two main control signals in such a manner as to equalize theoutput signals, the two amplification factors then being in the sameratio N, wherein the controller comprises a feedback circuit to controlthe value of one of the control signals to the difference between thetwo output signals.
 16. The main circuit according to claim 15 furthercomprising: a generator to generate a reference signal; and a dividercoupled to the output of the generator and configured to deliver thesaid reference signal divided by N, the input signal of one of theamplifiers being the reference signal and the input signal of the otheramplifier being the reference signal divided by N.
 17. The main circuitaccording to claim 15 further comprising: a generator to generate areference signal; and a multiplier coupled to the output of thegenerator and configured to deliver the said reference signal multipliedby N, the input signal of one of the amplifiers being the referencesignal and the input signal of the other amplifier being the referencesignal multiplied by N.
 18. The main circuit according to claim 15,wherein the feedback circuit further comprises: a generator to generatean intermediate signal representative of the difference between the twooutput signals; and a correction unit coupled to the generator andconfigured to effect a correction of the proportional-integral type onthe intermediate signal.
 19. The main circuit according to claim 18,wherein the correction unit also effects a correction of the derivativetype.
 20. The main circuit according to claim 15 further comprising: atleast two auxiliary circuits each comprising at least one auxiliarylinear amplifier with an amplification factor controllable by anauxiliary control signal, the auxiliary amplifiers of the two auxiliarycircuits respectively having the same structures as those of the twomain amplifiers, wherein the auxiliary control signals respectivelyassociated with the two auxiliary circuits are respectively producedfrom the main control signals respectively associated with the mainamplifiers of corresponding structures.